Had Haruko not been so worried and gone to pick up Kiichi, who knows how differently things might have unfolded. Sumiko would have finally been able to lay bare her true heart and feelings; even if the moment was fleeting, it would have been whole enough to potentially steer the tide toward a quieter, more peaceful resolution.
Instead, she’s left with a knot of pent-up emotions that missed their moment, derailed by jealousy over another; she’s trying once again to do something to tie Kiichi down, but her feelings have reached such a fever pitch that it risks escalating into even more extreme situations.
But then again, I guess if things had just gone smoothly, we probably wouldn't have a "manga" to read, lol.